Use of organically-modified clays (organoclays) has been investigated as a promising and potentially cost-effective method for removing organic contaminants from water. However, important questions remain regarding the chemical environment of the organoclay interlayer and how it influences contaminant uptake. In this work, hexadecyltrimethyl ammonium (HDTMA)-modified montmorillonites (STx-1b) were prepared at a range of HDTMA loadings, and batch sorption isotherms for a homologous series of substituted benzenes were conducted. Dry and water-saturated organoclays were characterized for HDTMA loading (total C analysis), interlayer spacing (X-ray diffraction), and HDTMA interlayer crystallinity (FTIR, ν<sub>as</sub>(CH<sub>2</sub>)). Interlayer spacing and crystallinity were also determined for organoclays containing sorbed contaminants. Our results suggest that HDTMA loading (primarily) and hydration (secondarily) influence the interlayer spacing and the relative crystallinity of the interlayer HDTMA. Sorption isotherms were generally Type III, indicating that aromatic contaminant uptake promoted further uptake, and exhibited significant sensitivity to HDTMA loading. Sorption initially increased with HDTMA loading, presumably due to the increased interlayer hydrophobicity and expanded interlayer. Sorption peaked at intermediate HDTMA loadings and decreased at yet higher organo-modification. We hypothesize this reversal in sorption trends is due to the highly crystalline paraffin-like HDTMA arrangement that dominates at high loadings. Contaminant uptake on mid-to-high loading organoclays was observed to disrupt HDTMA crystallinity proportionally to the amount of contaminant present, which supports our hypothesis that HDTMA crystallinity serves to restrict contaminant uptake and that contaminant sorption-induced decreases in HDTMA crystallinity produce the Type III isotherm. Future work will seek to develop optimized organoclays that maximize contaminant uptake by achieving interlayer expansion without increased interlayer crystallinity.

Influence of interlayer chemistry on uptake of aromatic contaminants to HDTMA-modified montmorillonite

254th National Meeting (2017)

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